1) Field of the Invention
This invention relates to dyes for color filters suitable for use in liquid crystal television sets, color image pickup tubes and color copying machines, photosensitive resist resin compositions containing the dyes, and color filters fabricated by curing the resin compositions.
2) Related Art of the Invention
Known fabrication processes of color filters include printing processes utilizing the principle of printing, dyeing processes and pigment printing processes, both making use of photolithography, and electrodeposition processes involving electrochemical deposition of a dye ("Nikkei New Material", 48-56 (Feb. 25, 1991)).
Fabrication of a filter by a dyeing process comprises, as shown in FIG. 1 by way of example, the following steps: (1) coating a glass substrate with a coating formulation which is formed of a water-soluble dyeable high-molecular material, such as gelatin or casein, and to which has been imparted photosensitivity by the addition of a bichromate, (2) exposing the thus-formed coating to ultraviolet rays through a photomask, (3) developing the thus-exposed coating to form a pattern, (4) coloring the pattern with an acid dye, (5) subjecting the thus-colored pattern to color-mixing protection, and (6) repeating steps (1) to (5) until the other two colors are applied to the glass substrate. The color filter obtained by the dyeing process has excellent pattern resolution and dimensional accuracy, superb light transmission and high lightness. Such a dyeing process is, however, accompanied by the following drawbacks:
(1) If the glass substrate is dyed with the second color without applying color protection subsequent to its coloration with the first color, the dye for the second color migrates into the filter layer of the first color so that the spectral characteristics are deteriorated. To avoid this problem, it is necessary to apply a color protection film with an acryl, urethane or epoxy resin or to subject the surface of the dyed medium to chemical treatment with tannic acid or the like.
(2) The heat resistance is insufficient due to the use of gelatin or casein as the base of the photosensitive resin.
On the other hand, fabrication of a filter by a pigment printing process makes use of a pigment which is employed for heat-resistant paints or for the coloration of plastics, and as depicted in FIG. 2 by way of example, comprises the following steps: (1) coating a glass substrate with a photosensitive resin containing a pigment uniformly dispersed therein, (2) exposing the thus-coated glass substrate to ultraviolet rays, (3) developing the thus-exposed coating to form a colored pattern, and (4) repeating the steps (1) to (3) until the other two colors are applied to the glass substrate. The color filter obtained by the pigment printing process has pattern accuracy as high as that obtained by the dyeing process and is also excellent in heat resistance and light resistance, but is accompanied by the following drawbacks:
(1) Its light transmission is inferior and its contrast is low, because light is scattered by the pigment particles.
(2) Prior to coating the photosensitive resin in which the pigment is uniformly dispersed, the resin should be passed through a filter to eliminate dust and large particles. Processing troubles therefore occur including clogging of the filter by coagulated pigment particles.
If the process shown in FIG. 2 is followed to fabricate a filter by using "M/P Pink REL" (trade name; product of Mitsui Toatsu Dyes, Ltd.) or "PS Green B" (trade name; product of Mitsui Toatsu Dyes, Ltd.), a resin-soluble conventional dye, instead of a pigment, the conventional dye is not immobilized in a matrix because its molecular weight is lower than 500. As a consequence, the dye may move to an adjacent matrix and cause color mixing. Further, the solubility of the conventional dye is insufficient so that the color filter must have a great film thickness in order to obtain a desired color density.
It is conceivable to immobilize a dye in a matrix resin using, as the dye, a reactive dye containing a monochlorotriazinyl group or a sulfatoethylsulfone group. Such reactive groups are however of the heat reactive type, thereby making it extremely difficult to fabricate micro-matrices like color filters. In addition, a salt remains in the resin after the reaction so that the electrical insulating property is impaired.